Rendering is the process of generating an image from a model, by means of software programs or electronic hardware. The model is a description of three dimensional objects in a strictly defined language or data structure. The model may contain geometry, viewpoint, texture and shading information. The image, produced from rendering, is a digital image or raster graphics image. ‘Rendering’ is also used to describe the process of calculating effects in a video editing file to produce final video output.
Rendering is one of the major sub-topics of 3D computer graphics, and in practice always connected to the others. In the graphics pipeline, it is the last major step, giving the final appearance to models. With the increasing sophistication of computer graphics since the 1970's onward, it has become a more distinct subject.
In computer graphics, shading refers to the process of altering a color of a surface based on its angle to lights to create a photorealistic effect. Shading is performed during the rendering process.
Flat shading is a shading technique used in 3D (three dimensional) computer graphics. It shades each polygon of an object based on the angle between the polygon's surface normal and the direction of the light source, their respective colors, and the intensity of the light source. A surface normal, or just normal to a flat surface is a three-dimensional vector which is perpendicular to that surface. A normal to a non-flat surface at a point p on the surface is a vector which is perpendicular to the tangent plane to that surface at p. The word normal is also used as an adjective as well as a noun with this meaning: a line normal to a plane, the normal component of a force, the normal vector, etc.
Illumination shading of surfaces (such as terrain) is typically accomplished through a set of vector calculations repeated for each point in the surface. When an application demands a changing orientation of the light sources, the calculations must be repeated.
This requires considerable computation resources for avionics systems where the light source moves dynamically with mid-flight heading changes. This light movement is required for human factors depth-cueing reasons. Correct depth cueing is best maintained with the dominant light source positioned approximately 45 degrees to the left of current heading and some fixed angle above the horizon. High-performance terrain rendering applications require complex shading models consisting of multiple light sources varying in direction, intensity, and chromaticity. The increased computational complexity adds to the cost and complexity of the system. For terrain representations, calculation precision must be relatively high to avoid a noisy appearance in smooth regions.
Therefore, it would be desirable to provide a method and apparatus to reduce computational resources and cost for light shading in high-performance terrain rendering applications.